The Mercury News

Dolphins, humans benefit from fishing collaborat­ion

- By Christina Larson Gary Richards, aka Mr. Roadshow, is off and will return in February.

A fishing community in southern Brazil has an unusual ally: wild dolphins.

Accounts of people and dolphins working together to hunt fish go back millennia, from the time of the Roman Empire near what is now southern France to 19th century Queensland, Australia. But while historians and storytelle­rs have recounted the human point of view, it's been impossible to confirm how the dolphins have benefited — or if they've been taken advantage of — before sonar and underwater microphone­s could track them underwater.

In the seaside city of Laguna, scientists have, for the first time, used drones, underwater sound recordings and other tools to document how local people and dolphins coordinate actions and benefit from each other's labor. The most successful humans and dolphins are skilled at reading each other's body language. The research was published Monday in the journal Proceeding­s of the National Academy of Sciences.

The Laguna residents work with wild bottlenose dolphins to catch schools of migratory silver fish called mullet. It's a locally famous alliance that has been recorded in newspaper records going back 150 years.

“This study clearly shows that both dolphins and humans are paying attention to each other's behavior, and that dolphins provide a cue to when the nets should be cast,” said Stephanie King, a biologist who studies dolphin communicat­ion at the University of Bristol and was not involved in the research.

“This is really incredible cooperativ­e behavior,” she added. “By working with the dolphins,” the people catch more fish, “and the dolphins are more successful in foraging, too.”

Dolphins and humans are both highly intelligen­t and long-lived social animals. But when it comes to fishing, they have different abilities.

“The water is really murky here, so the people can't see the schools of fish. But the dolphins use sounds to find them, by emitting small clicks,” much as bats use echolocati­on, said Mauricio Cantor, an Oregon State University marine biologist and study co-author.

As the dolphins herd the fish toward the coast, the people run into the water holding hand nets.

“They wait for dolphins to signal exactly where fish are — the most common signal is what locals call `a jump,' or a sudden deep dive,” said Cantor, who is also affiliated with the Federal University of Santa Catarina in Florianópo­lis, Brazil.

The more closely the people synchroniz­ed their net-casting to the dolphins' signals, the more likely they were to trap a large catch.

So what's in it for the dolphins?

The descending nets startle the fish, which break into smaller schools that are easier for dolphins to hunt.

 ?? DR. FÁBIO G. DAURAJORGE — UNIVERSIDA­DE FEDERAL DE SANTA CATARINA VIA AP ?? A dolphin jumps in front of fishermen at Praia da Tesoura, in Laguna, Brazil, in 2008.
DR. FÁBIO G. DAURAJORGE — UNIVERSIDA­DE FEDERAL DE SANTA CATARINA VIA AP A dolphin jumps in front of fishermen at Praia da Tesoura, in Laguna, Brazil, in 2008.
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